Apparatus for exchanging heat with subterranean regions



May29, 1951 .E-.LANY 2,554,661

APPARATUS FOR EXCHANGING HEAT WTH SUBTERRANEAN REGIONS Filed Jurie 20, 1947 5 Sheets-Sheet l May 29, 1951 Y G. E. CLANCY APPARATUS FOR EXCHANGING HEAT WITH SUBTERRANEAN REGIONS Filed June 20, 1947 3 Sheets-Sheet 2 i averi-a1 @im f1-'r 51am:

May 2 9, 195l G. E. cLANcY 2,554,661

` APPARATUS Fon ExcHANGING HEAT WITH SUBTERRANEAN REGIONS Filed June 2o, 1947 f :s sheets-sheet s R .Zr/ver: i'ar El-.lbgri'fz Diaw 15M@ Q/ S annif Patented May 29, 1,951

APPARATUS FOR EXCHANGING HEAT WITH SUBTERRAN EAN REGIONS Gilbert E. Clancy, Los Angeles, Calif., assigner toV Drayer-Hanson,

Incorporated, Los Angeles,

Calif., a corporation of California Application June 20, 1947, Serial No. 755,859

1 Claim. l

This invention is concerned generally with the use of the subterranean earth as a source of heat or as a sink in which to dissipate heat, and relates more particularly to means and methods for constructing apparatus, and the apparatus, by Which heat can be exchanged with subterranean regions economically and effectively.

Many possible -uses for such apparatus are well known. For example, in a refrigeration system heat is given up by the condenser and must be disposed of. The rejected heat is ordinarily transferred ultimately to some fluid medium Which is available in large quantities, such as atmospheric air or a stream of water, which is then rejected. The present invention makes it practicable to transfer heat, either directly or through an intermediate heat carrying medium, from the condenser of a refrigerating system to the non-fluid material of the underground earth. This is particularly advantageous wherever water is not available in abundance and when the temperature of the air is high. Since subterranean temperatures are relatively stable throughout the year, being usually far lower than average air temperature during the summer, the use of such regions forl heat disposal makes possible improved efficiency of operation of refrigeration equipment under such conditions.

Another illustrative example of the various possible uses for heat exchange apparatus in accordance with the present invention is in connection with reversed application of a refrigeration system for` heating, generally referred to as a reversed cycle system. In such a system heat must be supplied to the evaporator from some source outside the space to be heated. Atmospheric air is sometimes used as a source of heat for this purpose, but this may be too cold to permit the system to operate effectively. In winter the subterranean earth is usually much warmer than the average air temperature, and it is therefore potentially a better source of heat for a reversed cycle heating system.

An important difficulty in exchanging any appreciable quantity of heat in a given direction between a circulated `fluid, say, and subterranean regions is that the thermal conductivity of the earth is relatively low. Therefore if heat is to be transferred at a useful rate it is necessary either to maintain a relatively large temperature difference between the circulated fluid and the ground, which lowers the overall eiiiciency of the system, or to provide a large effective surface of thermal contact I cetweenl the iluid and the ground.

If vthe heat carrying fluid is circulated through the interior of a cylindrical shaft or pipe driven into the ground in the manner of an ordinary well casing, the necessary large area of thermal contact can be obtained, for example, by using a very deep shaft or by using a pipe of large diameter. Either of these expedients increases the cost of installation and operation to a prohibitive extent.

An important general object of the present invention is to enlarge the effective area of thermal contact between the surrounding ground and a well pipe or shaft of given length and diameter, thus increasing the rate of heat exchange for a given temperature difference. This general object is accomplished, according to one aspect of the invention, by providing a large number of side arms of heat conducting material which extend radially outward from the shaft into the surrounding earth. Because of the large area of contact between these arms and the ground and the high thermal conductivity of the arms as compared with that of the ground, heat exchange is greatly accelerated between the shaft wall and the entire volume of ground which is penetrated by the radial arms.y Accordingly, this volume of ground, which has the general form of a cylinder coaxial with the shaft, and has a diameter of the order of twice the length of the conductive arms, is brought substantially to the temperature of the shaft wall. The effective area of heat transfer surface between shaft and ground is therefore approximately given by the area of the cylindrical volume just described. This effective area exceeds the surfacearea of the shaft itself by a factor which is given approximately by the ratio of the arm length of the shaft radius. This factor is limited in practice by local conditions and other circumstances, but is typically between three and six. This factor represents a corresponding increase inrate of heat exchange for a given temperature difference between shaft and ground.

The above described heat conducting arms are projected radially into the ground, according to the invention, by axial motion of the shaft or well pipe through the ground in a particular direction. The arms are so mounted on the pipe that when this is moved axially in one direction, as in sinking the shaft into the ground, they lie closely against the exterior wall, offering little or no ob@ struction to its motion. When the shaft is moved in the opposite direction, as in lifting by a hydraulic jack or the like, the construction of the arms causes them to engage the surrounding ground and penetrate it in a generally radial direction. The operation of thus moving the shaft axially is simple and economical to carry out, so that the additional heat exchanging capacity is obtained with relatively little additional expense. Also, the operation is carried out with minimum disturbance in the immediately surrounding earth and a tight contact is obtained between the armed shaft formation and the earth, so that maximum heat conductivity between the metal formation and earth and through the earth is maintained.

Another object of the invention is to increase the heat conductivity of the ground itself and to improve the effective heat transferring contact between the ground and the surfaces of the pipe and arms by filling the interstices with water, silt, `or with material of relatively high heat conductivity.

The exact nature of the invention, as well as further objects and advantages thereof, will be understood from the following description of a preferred embodiment, which is intended as an illustration only and is not to be construed as limiting the scope of the invention. The attached drawings form a part of this description:

Fig. 1 is a fragmentary side elevation of a pipe equipped with side arms in accordance with the invention;

Fig. 2 is a transverse section taken on line 2-2 of Fig. 1;

Fig. 3 is an enlarged fragmentary side elevation showing a side arm is normal initial position;

Fig. 4 is an elevation similar to Fig. 3, but showing the side arm in collapsed position, as when the pipe is being driven into the earth;

' Fig. 5 is an elevation similar to Fig. 3, but showing an alternative side arm structure in normal position;

Fig. 6 is an elevation similar to Fig. 4, showing the alternative form of Fig. in collapsed position;

Figs. 7, 8 and 9 are schematic longitudinal sections, showing respectively a typical pipe equipped withside arms in positions fully sunk into the ground, partially raised from the latter position, and fully raised to spread the arms;

Figs. 10, 11 and 12 are transverse sections taken respectively as indicated by line Ill-I0 in Fig. '7, by line lI-ll in Fig. 8, and by line I2-I2 in Fig. 9; Y

Fig. 13 is a schematic longitudinal section showing means for circulating a fluid through the pipe of Fig. 9;

Fig. 13a. is a fragmentary section similar to Fig. 13, but showing modified fluid circulating means; and

Figs. 14 and l5 are sections similar to Fig. 13, but showing arrangements for using a subterranean pipe respectively as refrigerant condenser and evaporator.

According to the preferred modification of my invention here described for purposes of illustration, the pipe 20, whichhas been equipped with side arms 25 to be described, is sunk into the ground, indicated generally at 30, by any convenient method. For example, the ordinary procedure for drilling a Well may be used, pipe 20 then taking the place of the kusual outer well pipe or casing. In that instance the well hole is preferably m-ade of such size that the pipe with its arms in collapsed position will nt the hole snugly, even with a driving t. Or the pipe may be initially driven into the earth and the earth material subsequently removed from its interior.

Arms 25 are so constructed that they normally project upward and radially outward from pipe 20 in such .a manner as to form a barb-like structure; but can be collapsed closely against the pipe surface.

Arms 25 are here shown as elastic metal strips of blade-like form, preformed to give them a longitudinal curvature, pointed at one end 21 and connected at the other end 28 to the outside of pipe 20 in some good heat conductive manner, as by melding at 28a. Curved arms 25 are attached to pipe 20 with their convex sides towardthe pipe and extending generally parallel to the pipe from their point of connection toward the upper end 22 of the pipe, or toward what will be the upper end when the pipe is sunk into the ground. The plane of curvature of each bladelike arm is then an axial plane of the pipe, and the upper end of each arm normally projects radially outward from the pipe as an upward pointing barb.

Arms 25 are distributed more or less uniformly over the surface of the pipe from near its lower end 2| upward for a distance which depends upon local ground conditions andthe requirements of each installation, but which typically extends about two-thirds of the total length of the pipe. The exact arrangement of arms 25 on the pipe surface is subject to considerable variation, but an arrangement such as is shown illustratively in Figs. 1 and 2 has been found to give satisfactory results. The arms are shown arranged in circular bands 23 around the periphery of the pipe, the arms in each band being closely spaced, and adjacent bands being spaced along the length of the pipe at intervals which are approximately a third of the blade length. The arms in each band are in staggered relation with respect to the arms of the adjacent bands. In spite of this staggered spacing, which will be seen to produce a more uniform lnal distribution of the arms in the earth, there is considerable longitudinal overlapping of the arms along the length of pipe, as can be seen clearly in Fig. 1. This may of course be avoided, if preferred, by increasing the longitudinal spacing of the bands 23, but it is preferred in general to use the larger number of arms which results from a relatively close spacing, both transversely and longitudinally. The spacing can be made considerably closer than that illustrated.

The relation between the curvature of the arms and the elastic properties of the material from which they are made is such that when an arm is deflected from its normal projecting position (Fig. 3) into collapsed position substantially flat against the pipe surface (Fig. 4) the arm is not permanently deformed, but tends to resume its initial barb-like position. Due to the longitudinal overlapping of the arms, mentioned above, the upper portions of the arms when in collapsed position do not ordinarily contact the pipe, as is indicated in Fig. 4, but rest against the lower portions of the arms which are located immediately above them on the pipe. Since the arms are preferably relatively thin, however, their collapsed position is not substantially different whether there is such overlapping or not. For clarity of illustration, Figs. 3 to 9 show an arm arrangement in which no overlapping occurs.

The longitudinal curvature ofthe arm may be uniform over the length of the arm, or may be localized to a greater or less degree along this length. Thus,.for example, in Fig. 3 the lower portion of `blade 25. is shown substantially straight, the curvature being mainly confined to the upperl portion of the arm.

The spring action tending to move arms 25 into their barb-like position may be provided partially or wholly by spring means 4outside of the arms themselves. As an example, Fig. l5 shows an arm 25a which is itself straight, ybut the upper end of which is normally held Aaway from pipe by leaf spring 26. can be temporarily deflected into collapsed position by a radially inward force which flattens spring 26 as indicatedin Fig. 6. Y

Whether arms are normally straight'or curved, they are somewhat flexible `in a plane which is axial with respect: to the pipe, and are relativeily stiff in a direction normal to that plane. A convenient way of obtaining such characteristics is to form the arms from steel stock of fiat section, and to fasten their lower ends flat against the pipe surface. However, otherV types of crosssection may be used, including round, square, or flanged forms. Ordinary structural steel is a suitable material for the arms, the thermal conductivity of steel being roughly 4ten to one hundred times greater than that of earth, depending upon local conditions, including water content. Higher conductivity ratios can be obtained by forming the arms of some metal which has a particularly high thermal conductivity, such as aluminum alloy with suitable physical properties. A complex arm structure may be used, combining the properties of various substances. For example, the arm a in Figs. 5 and 6 is of laminar form. One layer, say 25h, can then be of a structural material such as steel, and the `other layer 25o of a material of particularly high heat conductivity but relatively low strength, such for example as copper.

Figs. 5 and 6 illustrate connection of the arms 25a to the pipe by means of a hinge structure 24, rather than by a rigid connection as in Figs. 3 and 4. A pivoted hinge such as 24 can be used with the straight type of arm 25a or with curved arms such as 25. Use of a suitably designed hinge reduces heat conduction between the pipe and the arms only slightly, and permits the latter to swing outwardly without depending entirely upon longitudinal flexibility.

When the arm end is rigidly connected to the pipe, the flexibility of the arm performs the function of a hinge, so that the arm can be considered to be hinged to the pipe whether a pivoted hinge such as 24 is introduced or not.

When pipe 2l] is sunk into the ground the pressure of the ground against the outer face of each arm as it descends below the ground surface 3l, collapses the arm against the pipe surface, so that the downward motion of the pipe is not appreciably resisted. The pipe is sunk to a suflicient depth to bring the uppermost of arms 25 well below the surface 3l of the ground. The pipe is then raised longitudinally by applying a suitable upward force to its upper end 22. This can be done, for example, by means of one or more hydraulic jacks which may act `directly upon a lug 3B or other iitting connected to the pipe, or may act as indicated schematically in Figs. '7 to 9 upon a lever 31 which is supported on a fulcrum 3B and engages lug 36.

As the pipe is raised from the lowest position to which it has been sunk (Figs. 7 and 10) the upper ends 21 of blade-like arms 25, urged outward from the pipe surface as has been de- The arm 25a scribed,k engage the ground immediately adjacent to the pipe, and are driven progressively farther into the ground in an upward and radially outward direction (Figs. 8 and 11). Pipe 20 is thus lifted, but not necessarily as an uninterrupted process, through a distance approximating the lengthV of the individual arms 25, or until the point 2'8 of connection of each arm to the pipe has been brought approximately to the level at which the upper end 2lv of that arm first penetrated the ground. The nal result, as indicated in Figs. 9 and 12, is to drive substantially the. entire length of each arm into the ground in` ari arc which is generally tangent to the pipe wall near the arm base 28 and curves upward and outward, becoming approximately horizontal near the arm tip 2l.

In practice itis found that the final position of arms 25 is somewhat irregular, sometimes including reverse curves at some points along the arm length, and usually including a fairly sharp bend .near arm base 28. However, the final position of the majority of arms is fairly illustrated by Figs. 9 and 12, which represent average final blade positions in average soil.

The two vertical dashed lines 38 in Fig. 9 and the dashed circle 39 in Fig. 12 indicate limits of the generally cylindrical volume of ground 40 which is penetrated by the formation of arms 25. The exact radius of this volume will depend upon many factors, but is seen to be roughly equal te the length of the individual arms 25. The finite radius of pipe 2li on which the arms are mounted at least partially makes up for the reduction in radial extent of the arms which results from their curvature.

Since the process of raising pipe 2D ordinarily bends the arms beyond their elastic limit, particularly near their bases 28, pipe 2i] is supported in its raised position (Fig. 9) by the arms so that no other permanent supporting structure is usually required. The upper end 22 of pipe 20 can then be cut off at any convenient height above or slightly below the ground surface 3|. The lower end of the pipe is preferably plugged as indicated at 44 in Fig. 13, after completion of the blade-spreading lifting process. The plug may be of any nature; for example, it may be threaded into an internal thread in the lower end of the pipe as shown, or it may be an expanded wooden plug, or may be formed by pouring a wet concrete into the pipe in proper quanltity to ll the lower end of the hole from which the pipe was raised.

Any suitable means can be employed for conveying heat between apparatus which is to be heated or cooled and the inside wall of pipe 20. For example, the interior of the pipe can be filled with a heat carrying fluid such as water, brine, or oil, and means provided for circulating this fluid through the pipe and through heat exchanging means above ground. Fig, 13 shows in schematic form a central inlet pipe 45, generally concentric with pipe 2E) and provided with nozzle-like openings 46 adapted to impart a strong tangential motion to fluid escaping through these openings into the annular space between the two pipes. The lower end of pipe 45 may either be closed, or have a constricted opening to deliver a jet downwardly. The resulting iluid motion insures effective heat exchange between the uid and the inner wall of pipe 29. A fluid outlet 49 is provided from the upper end of pipe 2li. A fluid circulating pump is indicated schematically at 5D and heat exchanging means are shown at 5l,

in which heat is supplied to or removed from the circulated fluid. For example, 5I may represent the condenser of a refrigerating system, the evaporator of a reversed cycle heating system, or any other means for which heat is to be removed or to which heat is to be supplied.

Alternatively, pipe 20 may itself be used as either condenser or evaporator in a refrigeration or heat pump system. Fig. 14 shows such use of pipe 20 as a condenser, compressed refrigerant vapor being admitted at 55 at the top of the pipe, condensing on the pipe wall to form liquid refrigerant 55, which is drawn olf from the bottom of pipe 2i) through outlet tube 51. Heat given up by the refrigerant upon condensation flows through the pipe wall and surrounding heat conductive arms 25 into the ground. With this arrangement the pressure difference between refrigerant vapor entering at 55 and fluid leaving at 56 must be sufficient to overcome the pressure head of 1luid in tube 5l and prevent re-vaporization of the condensed refrigerant at the reduced pressure which exists toward the top of this tube.

Fig. 15 shows schematically the use of pipe 20 as evaporator for refrigerant liquid which enters at 6U, preferably via a spray nozzle 6I, so that the liquid iiows down the walls of pipe 20 or falls in small droplets. Heat supplied from the surrounding ground to the pipe walls evaporates the refrigerant, the vapor leaving at 62.

In the examples given above, the heat carrying uid, whatever it may be, is circulated through the whole length of the pipe which includes of course that part of the pipe length that is surrounded by the heat conductive formation. In most instances such an arrangement seems to constitute the most convenient means of transferring heat to or from that part of the pipe which is in high conductive relationship to the surrounding earth. In some circumstances however, it may be desirable to limit the circulation, in its heat conductive relation to the pipe, to substantially that pipe portion which is surrounded by the heat conductive formation. For instance, that may be desirable where it is necessary to sink a relatively long pipe in order to reach an earth region of suitable temperature; and in such case it may be desirable to keep the fluid out of direct contact with the relatively long part of the pipe above the desired heat transfer zone, and/or to increase the flow velocity between that Zone and the ground surface. Fig. 13a is illustrative of such an arrangement applied for example to the circulation of an intermediate heat carrier such as water. Here the pipe 20 is shown as being plugged not only at its bottom but also at 44a at the upper end of its heat conductive formation. Input pipe 55a (corresponding to pipe 45 of Fig. 13) leads down through plug ida into the pipe interior below that plug; and outflow pipe 9a leads upwardly from the upper end of the space below the plug.

The rate of heat transfer between the surrounding ground and the well pipe, whether the latter is equipped with heat conductive side arms or not, depends greatly upon the nature of the ground itself, and particularly upon the amount of moisture present and upon whether the earth is in uniformly firm contact with the pipe and arm surfaces.

If the soil is porous, migration of underground water may be an important factor in determining the effective heat transfer capacity of a given installation. Such migration may be primarily a horizontal flow of water which exists independently of the presence'of the well 'pipefor it may be generally'verticalconvection brought about by thermal gradients caused directly by heat exchange with the pipe.' In either instance, the presence of heat conductive side arms such as 25 greatly increases the effectiveness of heat transfer between the pipe and the moving ground water.

In relatively dry ground, heat transfer results mainly fromordinary heat conduction, and tends to be accelerated by any change which increases the heat conductivity ofv the ground. Addition of water has such an effect, since water forms a bond between soil particles, increasing their effective area of contact. yAccording to the present invention, one or more small auxiliary pipes, as shown at l0 in Fig. 13, is sunk beside the main pipe 20, to which it may be attached as by welding. Auxiliary pipe 'In has small holes 'H in its wall, preferably distributed along at least that portion of its length which is adjacent the section of pipe 20 upon which blades 25 are mounted. Water is forced by means not shown down pipe 'l0 and out through openings 'H with sufficient pressure to saturate the surrounding ground with water. A continuous flow may be maintained, or the ground water may be replenished at intervals as required. Particularly when some continuous ilow is maintained, the heat exchange effected by the resulting movement of water in the ground may be appreciable. However, to obtain most of the required heat exchange by such flow will usually require an excessive amount of water. When only a limited supply of water is available, it can be used more effectively, as described, to increase the heat conductivity of the ground, rather than to transport heat directly.

' A more effective and also a more permanent way of increasing the heat capacity of the system is to introduce solid material into the interstices between the soil particles and more especially into the crevices between the soil and the pipe assembly which are formed during the process of sinking the pipe and raising it to spread arms 25. It has been found that when water is forced through auxiliary pipe 10, or through theopening at the bottom of main pipe 2l] before this is plugged, under sufficient pressure to bring some water to the surface along the outside of the pipe, silt is deposited by the water, filling most or all of the cracks between the ground and the pipe assembly. This procedure is more effective if a suspension of ne silt is washed through the pipe, instead of plain water. Alternatively, the washing procedure just described can be carried out through openings 13 which are provided in the Wall of pipe 20 itself, and openings such as 'I4 in sealing plug 44. Valves or other sealing means for the holes 13, 14 are provided, as shown schematically at 15, by which the openings are sealed after completion of the washing operation.

The above described procedure is made more effective by use of a suspension of particles of a :material with relatively high heat conductivity, such as a metal. Finely divided aluminum is an example of a suitable material for this purpose, since it has not only a high heat conductivity, but also a low density so that it can be carried relatively easily in suspension in water.

To obtain the full advantage of washing with a suspension, whether of ordinary silt or of some special material such as finely divided aluminum, the suspens-ion is preferably introduced into the ground under high hydrostatic pressure, so that it will drive out and replace whatever water is present, and will ll all interstices of the ground. Such pressure is preferably maintained for some time, whereby the ground surrounding the pipe acts as a filter for an appreciable quantity of the suspension, and the pores of the soil become gradually lled with the suspended material. This procedure is most eiective in sandy or gravelly ground, but even in ne clay it is valuable in filling cracks immediately surrounding the pipe assembly and improving heat transfer between the surfaces of the pipe and arms and the adjacent ground. The procedure is generally to be avoided, however, in locations where migration of ground water is to be expected, since it may reduce the permeability of the soil and hence the accessibility of the pipe assembly to such water.

I claim:

A heat exchange apparatus adapted for subterranean use, comprising in combination a pipe, structure forming inlet and outlet passages for a iluid heat exchange medium, said passages communicating with the interior of the pipe, and a plurality of elongated metal blades of ilat crosssection mounted on the pipe, one end portion of each blade lying atly against and in heat conducting relation to the outer surface of the pipe and rigidly connected thereto, the central portions of the blades extending freely from the respective points of said connection generally parallel to the pipe wall in a common axial direction, with the free blade ends yieldingly curved away from the pipe wall in axial planes, the

blades being arranged closely adjacent each other in transverse rows about the circumference of the pipe, the said rows being spaced from each other longitudinally of the pipe by such distance that the free portions of the blades of one row overlie at least the xed portions of the blades of another row, the blades being relatively flexible longitudinally in planes axial of the pipe and relatively stili1 longitudinally in planes normal thereto, all whereby the blade-carrying pipe may be sunk in the ground and then moved in the said axial direction to drive the carried blades radially outwardly into heat conducting relation with the surrounding virgin ground.

GILBERT E. CLANCY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Switzerland Feb. 13, 1912 Number Number 

